Most modern brake systems include a brake booster to multiply the driver's pedal effort as the brake pedal is depressed. When the brake pedal is depressed, low air pressure within a brake booster assists in depressing a master brake cylinder. More specifically, low air pressure within a vacuum chamber relative to a supply chamber causes forward movement of a diaphragm which, in addition to the brake pedal, pushes forward a brake cylinder piston.
Brake boosters require a source of negative pressure for the vacuum chamber. For gasoline engines, engine manifold airflow is typically used to generate negative pressure. However, many compact vehicles have somewhat smaller engines that lack the additional capacity to provide sufficient negative pressure for a brake booster. In these vehicles, it becomes necessary to provide a dedicated vacuum pump for the brake booster vacuum chamber.
Rotary vane pumps are a known category of vacuum pumps for brake boosters. Rotary vane pumps include rotating vane chambers between adjacent vanes. As the vanes rotate, the vane chambers vary in size to draw air from the inlet side of the pump to the discharge side of the pump, creating a source of negative pressure at the inlet side. The vanes are typically rotated by an electric motor within a pump housing.
Despite the advantages of rotary vane pumps, in some instances rotary vane pumps may generate a perceptible noise at specific frequencies. Accordingly, there remains a continued need to reduce the acoustic output of rotary vane pumps for use with brake boosters and potentially other applications.